The description tells me it's falling off the pad. It could be water logged foam. Normally, if you have enough power, you just push on through the chinewalk. Almost every boat does it at some point. Having the wrong prop pitch and type can make it more difficult to recover from but I would start your troubleshooting by adding a 100lbs of 00 buck shot to the port side seat (bagged of course). You can move it around until you find the sweat spot. Don't worry, no body will laugh at you. Ask any Allison owner what they do and you'll probably hear the same thing. I had an Alli XBT that took 75 lbs and a 2002 that took 125lbs.
A side note about the buck shot. If it is your cure, either make a permanent container for it or make sure you check the bag often. They tend to rot out and you end up with bb's rolling all over you boat..